Molecular-dynamics simulation of the structure and diffusion properties of liquid silicon

Abstract

Using molecular-dynamics methods and the activation-relaxation technique, we have investigated the inherent structure and diffusion properties of liquid silicon. With increasing density, the 52\ifmmode^\circ\else\textdegree\fi{} and 60\ifmmode^\circ\else\textdegree\fi{} peaks (attributed to long bonds) in the bond-angle distribution functions decrease in height, while the spread main peak (mainly related to the bonds containing covalent character) increases and moves towards the tetrahedral angle. The change in density does not give rise to a clear change in the diffusion constants. With the change of temperature, the diffusion coefficients obtained from the average mean-square displacement can be fitted by Arrhenius equation. The fit yields an activation energy of 0.92 eV and a pre-exponential factor of $30.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}{\mathrm{cm}}^{2}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1}.$ However, the activation energy, which is determined from the activation-relaxation technique using a Metropolis accept-reject criterion with a fictitious temperature of 0.5 eV, is in the range of 0.22 to 1.0 eV and shows a steep increase at low temperature. The very large pre-exponential factor suggests that the interatomic forces obtained from the Tersoff potential are very strong. The information obtained in this paper is consistent to some extent with the recent experimental results of some physical properties of liquid silicon.